[CP2K-user] Is it necessary to perform frequency calculations for the optimized geometry in cp2k?

[Mohammad Shakiba]

Hello everyone,

When optimizing with CP2K, we set a force limit and a maximum step size 
(for example less than 10meV and 0.002Bohr) and when the calculations 
reached those limits it is done. Before using CP2K I used Gaussian 09. When 
the geometry optimization was fully performed, I performed frequency 
calculation in order to check that there is no imaginary frequency so the 
optimization is not stuck in the local minima. However, when it came to big 
molecules, the rwf file tended to be hundreds of GB, so the calculations 
was not possible. Now, my question is:


Is it necessary to perform frequency calculations (like phonon calculations 
using phonopy) for the optimized geometry in CP2K? I mean the BFGS 
algorithm for geometry optimization is guaranteed to not stuck in the local 
minima? For example my system contains a quantum dot with many organic 
ligands (near 300 atoms) and the optimization is fully performed but I 
don't know if it would be acceptable to allege that this is the optimum 
geometry!  To sum up: when can we say that this is optimum geometry for 
this specific geometry configuration?

Thanks in advance. 
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